1. Technical Field
The present invention relates to a touch panel capable of suppressing the occurrence of Newton rings, and also relates to an electro-optic apparatus and an electronic device having the touch panel.
2. Related Art
Recently, small sized information electronic devices (hereinafter, it is referred to as electronic devices) such as PDAs (Personal Digital Assistant) and palmtop computers have become popular. Accompanied therewith, electro-optic apparatuses, in which a touch panel as a transparent input section is mounted on the liquid crystal apparatus (Liquid Crystal Display), have come into widespread use.
To make a high quality touch panel, it is necessary to suppress Newton rings (equal-thickness fringes having annular shapes that can be seen when flat glass sheets are brought into contact to each other) occurring on the panel input surface.
As techniques for suppressing the occurrence of Newton rings, for example, techniques disclosed JP-A-9-91091, JP-A-2002-287902, and JP-A-2004-280759 are known.
In JP-A-9-91091, transparent electrodes are provided on the inner surfaces of a pair of substrates, which are disposed to face each other with a predetermined gap provided therebetween, and a spacer particle group, which is formed of spherical spacer particles with diameters of 5 to 20 μm, is provided on one of these transparent electrodes, thereby suppressing the occurrence of Newton rings. In JP-A-2002-287902, a plurality of convex portions are substantially periodically formed with a pitch smaller than the wavelength of the visible light region on the at least one transparent electrode of the inner surfaces of the pair of substrates which are disposed to face each other with a predetermined gap provided therebetween, thereby suppressing the occurrence of Newton rings. Further, in JP-A-2004-280759, a pair of rectangular substrates (a front side substrate and a rear side substrate) are disposed to face each other with a seal material sandwiched between their whole circumference so that the whole circumference has a uniform gap, and the substrates are formed in a shape which is curved outward so as to have a height of 75 to 300 μm when the vertical and horizontal lengths of the front side substrate are in the range of 100 to 200 mm, thereby suppressing Newton rings which occur on the front side substrate.
However, in the techniques disclosed in JP-A-9-91091 and JP-A-2002-287902 mentioned above, it is necessary to form the plurality of convex portions and the spacer particle group on the inner surfaces of the substrates. Hence, there is a problem from the view of manufacturing cost.
According to the technique disclosed in JP-A-2004-280759, it is possible to achieve a reduction in manufacturing cost as compared with the techniques disclosed in JP-A-9-91091 and JP-A-2002-287902. However, in JP-A-2004-280759, while inclination is steep in the center region of the front side substrate, thereby suppressing the occurrence of Newton rings, inclination is slight in the vicinities of the corner portions (portions in which the adjacent side portions intersect each other) of the front side substrate to which a large binding force is applied due to the bonding with the seal material. Therefore, Newton rings tend to occur on the surface in the vicinities of the corner portions.